Powered device, using power over ethernet, with dedicated low current and high current paths for loads

ABSTRACT

In a method performed by a Power Over Ethernet (PoE) system, Power Sourcing Equipment (PSE) provides data and voltage over Ethernet wires to a Powered Device (PD). The PD converts the PSE voltage to a regulated voltage by at least one DC-DC converter in the PD. A first load in the PD, such as a processor, operates in a standby mode during a standby period and draws a low current from the converter via a low current path. During this standby period, a high current load in the PD is disconnected and does not draw current. When the first load comes out of the standby mode and into an active mode, the converter supplies a relatively high current to the second load and the first load. In this way, the first load, if a processor, can be already booted up at the time the second load becomes active.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority from U.S. ProvisionalApplication Ser. No. 61/714,057, filed Oct. 15, 2012, by David Dwelleyand Jeffrey Heath, incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to systems, such as Power Over Ethernet (PoE),where power is transmitted over data lines.

BACKGROUND

It is known to transmit power over data lines to power remote equipment.Power Over Ethernet (PoE) is an example of one such system. In PoE,limited power is transmitted to Ethernet-connected equipment (e.g., VoIPtelephones, WLAN transmitters, security cameras, etc.) from an Ethernetswitch. DC power from the switch is transmitted over two sets of twistedpair wires in the standard CAT-5 cabling. The same two sets of twistedpair wires may also transmit differential data signals, since the DCcommon mode voltage does not affect the data. In this way, the need forproviding any external power source for the “Powered Devices” (PDs) canbe eliminated. The standards for PoE are set out in IEEE 802.3,incorporated herein by reference.

Providing power over data lines is applicable to other existing systemsand future systems. For example, electronic equipment in automobileswill increasingly benefit from power to the equipment being providedover the data lines to reduce wiring. Various new systems using powerover data lines may be standardized by the IEEE or other groups.

Such systems using power over data lines may or may not requirehandshaking protocols.

Although some of the present inventions may be applied to any systemusing power over data lines, a typical PoE system will be described asan example.

FIG. 1 represents a typical Ethernet system using PoE. In the example ofFIG. 1, a “Power Sourcing Equipment” (PSE) 12 may be any Ethernet devicethat supplies power and data to a PD. The PSE 12 and PD 14 are typicallyconnected via a standard CAT-5 cable terminated with the standardEthernet 8-pin (four twisted pairs) connector. Only two of the twistedpairs are typically needed for PoE and data.

The PSE 12 is typically powered by the mains voltage (120 VAC) and useseither an external or internal voltage converter 16 to generate a DCvoltage between 44-57 volts. The PoE standards require the PoE to supplya minimum of 37 volts at the PD. The voltage drop along the cableincreases with distance.

Two of the twisted pairs 18 and 20 are assigned to carry the PoE power,and these pairs may also carry differential data. The remaining twopairs are also shown. All pairs in use are terminated at the PD 14 bytransformers, such as transformers 22 and 24. It is assumed that thetwisted pair 18 provides 44 volts and the twisted pair 20 is connectedto ground. A connection is made to the center tap of transformers 22 and24 to provide the 44 volts to the PD 14. Since the DC voltage is commonmode, it does not affect the differential data. Other conventionaltermination circuitry is also included in the termination block 25, suchas polarity correction circuitry, but is not relevant to the presentinventions.

The 44 volts is applied to a DC-DC converter 26 for converting thevoltage to any voltage or voltages required by the PD 14. The load 28(e.g., a security camera) is powered by the converter 26 andcommunicates with the PSE 12 via the twisted wire pairs.

The IEEE standards require certain low current handshaking proceduresbetween the PSE 12 and PD 14 in order to detect the presence of aPoE-powered device and in order to convey the pertinent characteristicsof the PSE 12 and PD 14 prior to the PSE 12 making the full poweravailable to the PD 14.

Below is a simplified summary of the handshaking protocol between thePSE 12 and the PD 14.

When a PoE-enabled Ethernet cable is plugged into the PD 14, the PSE 12interrogates the PD 14 to determine if it is PoE-enabled. This period istermed the detection phase. During the detection phase, the PSE 12applies a first current limited voltage for a fixed interval to the PD14, via the twisted wire pairs 18 and 20, and then applies a secondcurrent limited voltage for a fixed interval, while looking for acharacteristic impedance of the PD 14 (about 25K ohms) by detecting theresulting current. If the correct impedance is not detected, the PSE 12assumes that the load is not PoE-enabled and shuts down the PoEgenerating end. The system then operates as a standard Ethernetconnection.

If the signature impedance is detected, the PSE 12 moves on to anoptional classification phase. The PSE 12 ramps up the voltage to the PD14. The PSE 12 generates either one pulse (indicating it is a Type 1PSE) or two pulses (indicating it is a Type 2 PSE). The PD 14 respondsto the classification pulses with certain current levels to identifywhether the PD 14 is Type 1 or Type 2. A Type 1 PD requires less than 13W. A Type 2 PD requires up to a maximum of 25.5 W. Various classes(e.g., five classes), each associated with a maximum average currentlevel and a maximum instantaneous current level, within these types mayalso be identified. A classification resistance may be used. The PSE 12then may use this power demand information to determine if it can supplythe required power to the PD 14, and the PD 14 uses the information todetermine if it can fully operate with the PSE 12. There are maximumtime windows for the detection and classification phases (e.g., 500 ms).

Other types of detection and classification routines and standards maybe implemented in the future.

On completion of the detection and classification phases, the PSE 12ramps its output voltage above 42 V. Once an under-voltage lockout(UVLO) threshold has been detected at the PD 14, an internal FET isturned on. At this point, the PD 14 begins to operate normally, and itcontinues to operate normally as long as the input voltage remains abovea required level.

There are various opportunities in Ethernet systems and other systemsfor performing additional and alternative functions during thehandshaking phase, if any, and various other opportunities forperforming additional and alternative functions during the normaloperation of the PD.

Many of these opportunities arise as a result of such systems being usedin automobiles, where the powered components are predetermined by theautomobile manufacturer. Thus, it is unlikely that an incompatible partwill be connected to a socket in the automobile. Further, automobilesmay use a shared data/power bus to connect many PDs to a central switch,rather than use separate cables, to minimize wiring.

The terms PSE and PD are used throughout this disclosure to identifyequipment that supplies power and equipment that receives the power, andsuch equipment/devices are not limited to Ethernet equipment/devices.

SUMMARY

When an automobile begins operation, the automotive electronics,processors, memory, and other system functions must go through astart-up sequence. These system functions must begin the start-upsequence from either a low-power hibernation state, or a completelyunpowered state. A PD starting from an unpowered state may need to gothrough the IEEE PSE-PD handshaking protocol and complete its own powerup sequence for downstream electronics. All in all, the completeautomotive system power up sequence and boot-up can be time consumingand undesirable.

Additionally, it is common for a PD to have a low power standby mode, aspreviously described, so that time is not wasted booting up when the PDcomes out of the standby mode and draws a much higher current.

In accordance with an embodiment of the invention used in an automotivePower-over-Ethernet (PoE) system, a Powered Device (PD) is configured toprovide a dedicated power path to the low power load/standby circuitrywhile providing the option to disconnect the high power load in this lowpower mode of operation. Standby circuitry can include, but are notlimited to, memory, processors, etc. The standby circuitry can maintaininformation, provide processing functions, and retain start-upinformation while operating in a low-power state. Using the informationretained in the standby circuitry may significantly reduce boot up timeand start-up delay.

This invention is further described in the section labeled, PD HasStandby Power Path To Low Power Components and High Power Path to HighPower Components.

Various other techniques are disclosed herein that add functionality tosystems where power is provided over data lines. Some of thesetechniques occur during the handshaking periods between the PSE and thePD. Some of the techniques are particularly suitable for Ethernet andnon-Ethernet systems in automobiles where the PSEs and PDs arepredetermined by the automobile manufacturer so that the handshaking maybe abbreviated or dispensed with. The various techniques may becompatible with the current IEEE standards for PoE and anticipatedfuture IEEE standards.

Techniques are disclosed that:

Enable systems that supply power over data lines to be used inautomobiles by providing a boost converter in the PSE to boost the 12volt battery voltage to, for example, the 44-57 volts required by theIEEE PoE standards;

Limit in-rush current into a PD or a PSE when the PD or PSE is connectedto a power bus that may supply power to other PDs or PSEs, thus enablinghot-swapping;

Enable the programming of the PSE or PD power supply output voltagelevel for accommodating different types of PDs;

Enable the PSE to detect the actual voltage at the PD despite anunpredictable voltage drop along the cable;

Enable non-standard functions to be performed during the allowablehandshaking period when power-requirement information is already knownabout the PSE and PD;

Enable the handshaking delay to be avoided at each powering up time bystoring previously detected handshaking information in a memory;

Provide a specified low voltage by the PSE to the PD when requested,such as during a low power standby mode of the PD, that can be regulatedby an efficient (at low power) low dropout (LDO) regulator in the PDinstead of a less efficient switching mode regulator;

Enable the PSE to determine whether there are no PDs on a bus or anynumber of PDs on the bus;

Enable power to be transmitted to a PD using only one twisted wire pairof the data cable (e.g., Ethernet cable);

Provide a security feature that detects if a PD is connected to a properPSE and, if no detection, prevents operation of the PD;

Provide a security feature that periodically detects if a PD has beenremoved from the system and, if so, initiates a security routine;

Provide a low power standby path in the PD to supply power to low powerquiescent circuitry (e.g., memory, processor, etc.) in the PD to avoiddelays in starting up such circuitry;

Enable fast collision detection on a data bus by detecting the sums ofcombined signals on the bus; and

Enable fast terminating of traffic on a data bus in the event that ahigh priority message needs to be sent by summing concurrentlytransmitted signals to create an emergency “ALL STOP” signal. The highpriority message is then sent.

Various other embodiments are described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional PoE-enabled Ethernet system.

FIG. 2 illustrates a PSE with a boost converter for converting anautomobile's 12 volt supply to, for example, the standard 44-57 volt PoEsupply.

FIG. 3 illustrates a DC-DC converter in a PD or PSE having a soft-startcircuit for limiting in-rush current when the PD or PSE ishot-swap-connected to a power bus. The converter may be a step up orstep down converter.

FIG. 4 illustrates a programmable boost and/or buck converter in a PSEor PD.

FIG. 5A illustrates one method for supplying a programmable outputvoltage of the PSE or PD.

FIG. 5B illustrates another method for supplying a programmable outputvoltage of the PSE or PD.

FIG. 6 illustrates a PSE or PD with a controllable hot-swap switch thatis closed once the converter in the PSE or PD has ramped up toapproximately the power bus voltage to avoid in-rush currents.

FIGS. 7A and 7B illustrate a technique for allowing the PSE to determinethe actual voltage at the PD.

FIGS. 8A and 8B illustrate a technique for using the low current duringthe handshaking phase to detect signature information in an ID circuitin the PD to identify pertinent characteristics of the PD or to start upother low power circuitry in the PD.

FIG. 9 illustrates a method for storing the PD characteristics in amemory after an initial powering-up to avoid the need for repeating thefull handshaking protocol upon subsequent powering-ups.

FIG. 10 illustrates the PSE providing a programmable low voltage/powersignal to the PD during a low power standby mode of the PD to enable theuse of an LDO regulator in the PD to improve efficiency.

FIG. 11 illustrates a technique where a PSE connected to a power bus candetermine whether no PD is connected to the bus or whether an unknownnumber of PDs are connected to the bus.

FIG. 12 illustrates a PSE connected to a power bus and multiple PDsconnected to the bus, where the power (e.g., PoE) is provided over onetwisted wire pair in the cable and an external conductor.

FIGS. 13 and 14 illustrate a security technique wherein, only if aproper PoE protocol or other standard protocol is performed is anenabling circuit in the PD triggered for allowing the PD to operate.

FIG. 15 illustrates a security technique that periodically detectswhether a PD is connected to the PSE, either before the PD is powered upor after it is powered up and, if not, then initiates a securityroutine.

FIG. 16A illustrates a technique for the PD to provide a dedicatedstandby power path to low power components in the PD and provide aseparate high power path to the load when the PD comes out of thestandby mode.

FIG. 16B illustrates that the voltage converter in FIG. 16A can compriselow current and high current converters.

FIG. 16C is a flowchart identifying certain steps performed by thecircuit of FIG. 16A.

FIGS. 17A, 17B, and 17C illustrate how the signals from multiple PDsconnected to a power bus may be summed and the summed signals detectedto determine whether a collision has occurred, requiring retransmission.

FIG. 18 illustrates a technique for quickly issuing an ALL STOP signalto all PDs on a bus, without having to wait for the bus to be idle, inorder to transmit a high priority message on the bus.

Elements that are the same or equivalent are labeled with the samenumeral.

DETAILED DESCRIPTION

The various circuits shown represent the pertinent aspects of a system,such as a PoE-enabled Ethernet system, where power is supplied over datalines.

It is predicted that more and more of an automobile's electrical systemwill conduct data and power via a shared bus, such as a PoE-enabledEthernet bus. The systems may have to conform to IEEE standards forcompatibility. Using a shared data and power bus reduces wiring andallows a central means of monitoring the status of the various systems.Many other benefits can be realized. Accordingly, new techniques thatare directed to such automobile applications are very valuable. Thetechniques described herein are also applicable to non-automobileapplications.

Boost Converter in PSE for Automobile Applications

A typical PSE receives power from the mains voltage (120 VAC) andcontains (or uses) a step down regulator to provide voltage to the PD,such as the 44-57 VDC standard voltage for PoE. For automobileapplications, the power supply is typically a 12 volt battery; however,other battery voltages are also used and anticipated in the future.

FIG. 2 illustrates a PSE 30 receiving power from an automobile's 12 voltbattery 32. Any type of boost converter 34 is employed in the PSE 30 forconverting the 12 volts to a boosted output voltage, such as 24 volts orthe standard 44-57 volt PoE supply. The PSE 30 may be connected to a PD36 in the automobile using a cable or a bus. If the system is anEthernet system, the conventional PoE protocols and data communicationmay then be in accordance with the IEEE standards or in accordance withthe other techniques described herein. The PD 36 may be any load in theautomobile which uses power over data lines.

For automobiles with power supplies other than 12 volts, the converter34 boosts the supply voltage to any desired voltage.

Soft Start Circuit in PD or PSE Converter for Hot-Swapping

FIG. 3 illustrates one of the possible embodiments of a DC-DC converter38 in a PD 40, where the converter 38 has a soft-start circuit forlimiting in-rush current from a power bus 44 supplying an input voltageVin, such as an Ethernet bus, when the PD 40 is hot-swap-connected tothe bus 44. The converter 38 in the example is a boost converter but mayinstead be a step down converter. The converter 38 may betransformer-isolated from the input voltage source. Hot-swapping refersto the ability to replace a part without having to shut down the system.The ability to hot-swap enables, among other things, redundancy and highreliability. Multiple PDs 40 and 42 are shown in FIG. 3 connected to thebus 44, where the shared power/data cables are illustrated by a singleline for simplicity. In the example of PoE, the PoE cables are typicallytwo twisted wire pairs.

During a hot-swap event, an initially un-powered PD 40 is plugged into asocket, connected to the bus 44, which then supplies Vin (e.g., 44volts) to the PD's converter 38 for powering up the PD 40. It is assumedthat there are other PDs on the bus 44 already connected to Vin. It isimportant that there be no significant transients on the bus 44 (such asa lowering of bus voltage due to in-rush currents) when a PD is pluggedin, since a sudden drop in Vin may cause the other PDs connected the bus44 to not operate properly.

The Vin is applied to a low power LDO 46 (or other converter) in the PD40 for supplying a low operating voltage (e.g., 5 volts) to the variouscomponents forming the control portion of the converter 38.

If a conventional PD 40 were simply plugged into the bus 44, alreadypowering PDs on the bus, the converter 38 would initially draw themaximum current at a 100% duty cycle to quickly ramp up its outputvoltage Vout to the nominal voltage. This in-rush current wouldtemporarily lower the voltage Vin on the bus 44 and possibly cause theother PDs connected to the bus 44 to enter their undervoltage lockoutmode.

To limit the in-rush current into the converter 38 from the bus 44supplying Vin when a PD is first connected to the bus 44, a soft startcircuit is provided in the converter 38 to limit the duty cycle. Such asoft start circuit may directly limit the current through the powerMOSFET 52, as shown by the soft start current limit circuit 54, or thesoft start circuit may limit the threshold voltage Vth, as shown by thesoft start Vth ramp circuit 56. The level of Vth directly determines theduty cycle of the MOSFET 52. The circuit 56 relatively slowly ramps upVth to limit the duty cycle to avoid any transients in the Vin supply.The soft start circuit has no effect after the output voltage hasreached its nominal voltage.

Briefly, the MOSFET 52 is turned on at the beginning of a switchingcycle, clocked by an oscillator 57. This charges the inductor 58 andconducts a ramping current through a current sense resistor 59. Thelevel of Vout is fed back as a feedback voltage Vfb by a resistordivider 60 or a third winding of an isolation transformer. An erroramplifier 62 (a transconductance amplifier) and capacitor 64 generate athreshold voltage Vth necessary to keep Vfb equal to a reference voltageVref 66. When the ramping voltage across the resistor 59 crosses Vth, aPWM comparator 68 turns off the MOSFET 52 and turns on a synchronousrectifier MOSFET 70. The inductor 58 is then discharged to charge theoutput capacitor 48. When Vout is close to the desired output voltage,no more current limiting is required. Other soft start circuits andtechniques are envisioned.

In the event that the PD 40 was hot-swap connected to a common output47, the output capacitor 48, for smoothing ripple, should be preventedfrom drawing an in-rush current from the output bus 47. When Vout isdetected to be approximately equal to the voltage on the bus 47, thehot-swap switch 50 is closed to connect the converter 38 to the bus 47.

In another embodiment, the soft start circuitry is incorporated into theconverters of PSEs (rather than PDs) so that hot-swapping of a PSE to apower supply bus does not cause a transient that temporarily lowers thebus voltage. In such an embodiment, the bus 44 supplying Vin may beconnected to a battery.

Many other types of converters may be used, including step downconverters.

Programmable Voltage Converter in PSE or PD

Although the current IEEE standard for PoE is 44-57 volts, futurestandards may allow for different ranges of voltages. For non-PoEsystems, any output voltage may be specified. Therefore, in future PoEsystems and in non-PoE systems, the PDs may use input voltages such as12, 18, or 24 volts. In order for a single PSE to be usable for avariety of PDs with different input voltage requirements, the PSE'sinternal converter may be programmable by external signals or by othermeans.

FIG. 4 illustrates a programmable boost and/or buck converter 70 in aPSE 72. The output voltage Vout may be programmed by externallygenerated signals on input pins 74. In one embodiment, the programmingadjusts the feedback voltage Vfb in order to set Vout.

FIG. 5A illustrates one method for supplying a programmable outputvoltage of the PSE 75. In FIG. 5A, the programming signals on pins 74enable different voltage converters 76, 77, 78, which may include anycombination of step-up and step-down converters, for outputting thedesired voltage. A hot-swap switch 80 is shown, which allows the PSE 75to be connected into a “hot” PoE-enabled Ethernet bus or other power buswithout any significant in-rush current to avoid transients on the bus.

FIG. 5B illustrates another method for supplying a programmable outputvoltage of the PSE 81, where any number of voltage sources 82, 83, and84 may be connected in series via programmable switches 85, 86, and 87by signals applied to pins 74.

In FIGS. 4, 5A, and 5B, the adjustable-output converters may instead beincorporated in PDs to programmably adjust the converters' outputvoltage for a certain PD load. In such a case, the PD power suppliesneed not be replaced when replacing a PD load requiring anotheroperating voltage. The output voltages of the PD converters may beprogrammably adjustable to be, for example, 12 volts, 5 volts, and 3.3volts. The adjustable converters will typically be step down converters.

In another embodiment, the converters in both the PSEs and the PDs areprogrammably adjustable.

Hot-Swap Switch in PSE or PD

If multiple PSE's are connected to a PoE-enabled Ethernet bus or otherpower bus, they ideally should be able to be replaced without poweringdown the system. When a new PSE is then connected to the bus, thereshould not be any significant transient in the power path. Further, forPoE systems, for example, the IEEE standards set a limit on the currentthat can be supplied by the PSE. That current limit is about 400 mA fora Type 1 PSE and about 825 mA for a Type 2 PSE. The PD in-rush currentmust not exceed those limits or else the PSE is required to stopproviding power to the bus.

FIG. 6 illustrates a PSE 90 with a controllable hot-swap switch 92 (ap-channel MOSFET) that is closed once the converter 94 output voltageVout has ramped up to approximately the bus voltage Vbus to avoidin-rush currents. For PoE, that bus voltage may be about 44 volts. Theconverter 94 may be the same as that shown in FIG. 3. The feedbackcircuit of FIG. 3, connected to sense Vout, is not shown in FIG. 6 forsimplicity. In one embodiment, the power supply is a 12 volt battery inan automobile and the system is a PoE-enabled Ethernet system, so theconverter 94 is a boost converter for supplying at least the 44 voltsPoE minimum voltage.

The body diode 96 of the hot-swap switch 92 and the open state of theswitch 92 block current flow between the bus 98 and the converter 94until the Vout is approximately equal to the bus voltage Vbus. This isdetected by a voltage detector 100, such as a comparator or othercircuit. When Vout is equal to Vbus, the voltage detector 100 closes aswitch 102 to supply a ground voltage to the gate of the switch 92 tocause the switch 92 to conduct and couple the Vout terminal to the bus98.

A similar arrangement may be provided for hot-swapping PDs onto a PDload power bus. In such a case, multiple PD power supplies may be usedto power a single PD load. The PD power supply only is coupled to the PDload power bus when that PD power supply is generating a voltage aboutequal to the power bus voltage. This prevents the PD power supply frompulling down the PD power bus voltage due to in-rush currents.

PSE Senses Actual Voltage at PD

The IEEE standards for PoE require, for example, that at least 37 voltsbe supplied at the PD. Other voltage standards may be set in the future.Therefore, the PSE must supply greater than 37 volts to ensure that,despite a worst case voltage drop along the cable, the voltage at the PDwill not go below 37 volts. Providing anything more than 37 volts at thePD may be inefficient. The voltage drop is affected by the length of theEthernet cable or bus, which is unknown to the PSE. It would bedesirable to adjust the PSE output voltage such that the voltage at thePD is slightly greater than 37 volts to maximize efficiency.

FIGS. 7A and 7B illustrate a technique for allowing the PSE 104 todetermine the actual voltage at the PD 106. The technique may beperformed during the handshaking phase. Although the technique isdescribed with respect to an Ethernet system, the technique can beapplied to any system where power is applied over data lines.

PoE-enabled PDs have a 25K ohm resistor 108 across the PoE terminals toallow the PSE to detect that the PD is PoE-enabled during the detectionphase of the handshaking protocol. The PD's may also have a capacitor109 with a known value coupled across the PoE terminals.

In step 110 of FIG. 7B, the PSE 104 is connected to the PD 106.

In step 111, a controller 112 in the PSE 104 controls a detector/currentsource circuit 114 to supply a known low current (e.g., 100 mA) throughthe PoE wire pairs 116. The resulting voltage across the wire pairs 116at the PSE 104 will be the current multiplied by the combined seriesresistance of the resistor 108 and the wire pairs 116. However, theresistor 108 to wire resistance ratio may be too high to get an accuratedetection of the added resistance by the wires. An alternative techniqueis to generate a current pulse (an AC signal) by the circuit 114. Thecapacitor 109 across the PoE terminals of the PD 106 conducts the ACsignal with a very low impedance, which makes the ratio of the capacitorimpedance to the wire impedance low. This enables a more accuratedetection of the wire resistance. The resulting voltage at the PSE isthen detected (step 118). Since the impedance of the capacitor 109 inresponse to the pulse is known, the contribution of resistance by thewires can be determined using Ohm's Law. The resistance of the wirepairs 116 is then determined in step 120. Thus, the actual voltage dropalong the wire pairs 116 may now be determined at any current level(V=IR). The resistance or voltage drop is then stored in a memory in thePSE 104.

In step 122, the PSE 104 adjusts its voltage converter (e.g., a boostconverter) to compensate for the actual voltage drop along the wirepairs 116 at the present current level or at the maximum current levelallowed for the PD type. The result is an increased efficiency due tothe PSE 104 not supplying excess voltage at the PD 106. The PD usuallyswitches out the 25K ohm resistor after the handshaking phase to reducepower loss.

In future PoE systems, the 25K ohm resistor 108 may be eliminated orchanged, but there will still be some known input impedance (e.g., dueto a known capacitance) associated with the PD. In such cases, theabove-described technique is modified to take into account the actualinput impedance of the PD when determining the voltage drop along thewires between the PSE and PD.

The above technique applies to non-PoE systems as well, where a voltagedrop test is initially performed followed by adjusting the outputvoltage of the PSE to improve efficiency.

If the voltage applied to the PD is close to the voltage needed by thePD load, a LDO regulator may be used in the PD. For low currents, suchan LDO regulator may be more efficient than a switching regulator. Thevoltage supplied to the PD may be any voltage level if there is norequirement to comply with IEEE standards specifying voltage levels.

Use Low Current from PSE During Handshaking Phase to PerformNon-Standard Operations by the PD

The IEEE PoE standards require certain low current operations beperformed during the PSE-PD handshaking phase. A similar handshakingprotocol may also be standardized for non-Ethernet systems using powerover data lines. While the PSE is supplying the low current signalsduring the handshaking phase, such low current signals may also be usedfor additional functions by the PD. The handshaking protocol may beunaffected.

FIGS. 8A and 8B illustrate a technique for using the low current duringthe handshaking phase to detect signature information in anidentification (ID) circuit 126 (or other circuit) in the PD 128 toidentify pertinent characteristics of the PD 128. The additionalfunctions may all be performed within the allowable handshaking periodset by any IEEE standards (step 130 in FIG. 8B). Alternatively, or inaddition, the low current supplied during the handshaking phase may beused to power up any low power circuit in the PD, such as a datareceiver, processor, or memory.

In addition to the conventional detection phase, where the PSE 129provides a low current to detect the presence of the 25K ohm resistor132 across the wire pairs 134 (assuming a PoE-enabled system), the PD128 uses some of the current to address or otherwise detect informationin the ID circuit 126 (such as a memory circuit or an analog circuit).The ID circuit 126 may be high impedance so as not to affect thedetection of the 25K ohm resistor 132 by the PSE 129. The informationprovided by the ID circuit 126 is then transmitted over the wire pairs134 and stored in a memory 136 in the PSE 129. The process is controlledby a controller 138, controlling detection and power source circuitry140.

The ID circuit 126 may instead be any other low current circuit where itis desirable to start up the circuit during the low current handshakingphase rather than wait for the PD to become fully operational. Forexample, the circuit 126 may be a processor that is booted up during thehandshaking phase so it is ready as soon as full power is supplied bythe PSE to the PD.

Any other non-standard operation using the low current PSE 129 signalsare also envisioned (step 142). The information obtained from the PD 128may identify any class of the PD, any current levels needed, or otherinformation that may be of use by the PSE 129, such as for budgetingpower.

In step 144, the handshaking phase is completed and the PSE 129 providesthe PoE (or other power) to the PD 128.

In controlled communication systems, such as in an automobile, whereonly compatible components are provided by the automobile manufactureror are designated, there is no need for the full handshaking protocol,such as identified by the IEEE PoE standards. The IEEE PoE standards forhandshaking are designed to avoid supplying power to incompatible PDs.If it is assumed that the PDs are already PoE compatible (or compatiblewith another system used by the automobile) and their characteristicsare known, the full handshaking period may be used for obtaining anyinformation from the PD (via digital or analog signals). If the IDcircuit 126 is an analog circuit, the information may be conveyed by aresistance value, a current value, a voltage value, an RC time constant,etc.

Delete Detection Phase of Handshaking if Controlled System

In the case of an automobile electrical system or other system where theselection of the components are tightly controlled, it would already beknown whether the components are compatible or incompatible withreceiving power over the data lines. In such a case, the detection stepin the handshaking protocol may be deleted. Therefore, the handshakingphase may be abbreviated or dispensed with all together. In oneembodiment, the handshaking protocol only includes a low current phasethat detects a particular signal from the PD identifying the requiredpower of the PD to ensure the PSE can supply the required power to thePD. The low current phase may therefore simultaneously detect therequired power level as well as ensure the PD is capable of receivingpower over its data lines. This may be required for safety purposes toprevent the PSE from supplying a high current across shorted wires.

Save Handshaking Information in Memory at PSE after the Initial PoweringUp of the System

Conventionally, the handshaking phase between the PSE and the PD isperformed each time the system is powered up or a PD is connected. Itwould be desirable to speed up the time that the PSE and PD are up andrunning by obviating the handshaking phase or by only requiring asimpler handshaking protocol.

FIG. 9 illustrates a method for storing the PD characteristics in amemory after an initial powering-up to avoid the need for repeating thefull handshaking protocol upon subsequent powering-ups. In the example,it is assumed the system is a PoE enabled Ethernet system, but thetechnique is applicable to non-Ethernet systems.

In step 150 of FIG. 9, the conventional PoE handshaking routine isperformed where the PSE ascertains whether the PD is PoE-enabled and theclass/type of the PD.

In step 152, the pertinent PD characteristics (or other characteristics)obtained during the handshaking phase are stored in a memory in the PSE.FIG. 8A illustrates a PSE 129 containing a memory 136 and a controller138 that may be used for this process as well.

The PSE and PD may now operate normally with the PSE supplying PoE tothe PD.

When the Ethernet system is powered down, such as when an automobile isturned off, the PD characteristics remain stored in the memory, which ispreferably a non-volatile memory.

In step 154, when power is again applied to the PSE (or multiple PSEs),a controller in the PSE accesses the memory to determine the PoEcharacteristics of the PD rather than taking the time to perform theconventional handshaking routine. Thus, the handshaking routine isavoided, saving time. The information in the memory may instead allow asimpler and faster detection protocol to be used rather than obviate thedetection phase all together.

In step 156, the PSE(s) apply PoE (or other power) to the PD(s) via thedata lines.

PSE Provides Low Voltage Signal to PD During a Standby Mode of the PD toImprove Efficiency

Many types of PDs are not fully active when powered up but are in astandby mode where only some low power electronic components are poweredup. For example, the main load in the PD may not be turned on while alow power controller or processor in the PD is powered so as not torequire a time-consuming booting up when the main load is to be turnedon. Such low power standby components may only require 5 volts and a fewmilliamps. If the PSE supplied the full 44 volts (or a non-PoE voltage)to the PD, the PD voltage converter (typically a switching regulator)would be using energy to supply the low power to the standby componentsfor a relatively long time. The converter may even be the largest userof power during standby mode. Since standby periods are typically muchlonger than the periods when the load is fully on, there is significanttotal power usage during the standby period.

FIG. 10 illustrates a PSE 160 providing a low voltage (e.g., 5-12 volts)to the PD 162 during a low power standby mode of the PD 162. In anotherembodiment, the low power is provided anytime the PD 162 requests thelow power; however, a standby mode is given as an example. The PD 162generates a standby mode signal that is transmitted to the PSE 160 viaany of the Ethernet wire pairs (or other wires if Ethernet is not used)to initiate sending of the low voltage. A controller 170 in the PSE 160then controls one or more voltage converters or constant voltage sources172 and 173 to output the low standby voltage (e.g., 5 or 12 voltsinstead of the full 44 volts) on the PoE wire pairs, slightly more thanrequired by the standby mode circuit 166. The standby voltage may beprogrammable by the PD signal, or by programming pins of the PSE 160, orby any other means. Since there is low power, the voltage regulation inthe PD 162 during the standby mode may be performed by an efficient LDOregulator 164. Since the LDO regulator 164 does not switch but justcontrols a resistance element (e.g., a series MOSFET), the LDO regulator164 is much more efficient than the switching regulator 174 at such lowpower. The higher power switching regulator 174 in the PD 162 is turnedoff or in a sleep mode to prevent high frequency switching during thestandby mode to save power. Accordingly, efficiency is improved.

When the standby mode is ended, a standby signal is sent to the PSE 160and the full 44 volts is sent to the PD 162. The switching regulator 174then regulates the voltage for the higher power load. The system may beused with any non-PoE systems where power and data are delivered overthe same lines.

Technique to Determine Whether there are No PDs Connected to Bus orWhether there are One or More PDs Connected to Bus by Detecting anImpedance on the Bus

In the conventional detection phase of PoE, the PSE supplies a lowcurrent and determines whether the PD has a 25K ohm resistor across thewire pair. If so, this signifies that the PD is PoE-enabled. However, ifan Ethernet bus is used and any number of PDs may be connected to thebus, their 25K ohm resistors will be connected in parallel and present acombined low resistance. This low resistance will be below the allowableresistance specified by the IEEE standards for designating a PoE-enabledPD. This premise is presented in step 176 of FIG. 11.

FIG. 11 illustrates a technique where the PSE may determine whetherthere are any PoE-enabled PDs connected to an Ethernet bus. In acontrolled application, such as an automobile application, it would beknown that either all PDs connected to the bus are PoE-enabled or allPDs connected to the bus are not PoE-enabled. If the PDs arePoE-enabled, they will each have the 25K ohm resistor across the wirepairs. If there are no PDs or the PDs are not PoE-enabled, they willpresent an open circuit during the detection phase.

In step 178 of FIG. 11, during the detection phase, the PSE supplies alow current to the PoE wire pairs and detects either an open circuit orsome impedance greater than zero. If an open circuit is detected, thePSE will not supply any power. If an impedance greater than zero isdetected, the PSE assumes that all of the PDs connected to the bus arePoE-enabled, and the PSE applies the PoE to the bus (step 180).

This technique applies to non-PoE systems as well where a PD impedanceis used to determine whether a PD is connected to a bus. In such non-PoEsystems, the existence of no PDs on the bus is determined by detecting avery high impedance, and the existence of one or more PDs on the bus isdetermined by detecting an impedance equal to or less than the impedanceof a single PD.

Technique to Determine Whether there are No PDs Connected to Bus orWhether there are One or More PDs Connected to Bus by DetectingCollisions on the Bus

In another technique for detecting whether there are one or more PDs onan Ethernet bus or other bus is to detect whether there are anycollisions on the bus during the handshaking phase or during normaloperation. If the PSE generates signals on the bus for reception by anyPDs on the bus, and the signals from the one or more PDs on the bus areconsistent with a single PD, then the PSE knows that there is only onePD on the bus. If there are no return signals, the PSE knows that thereare no PDs on the bus. If the return signals are out of the expectedrange of signals from a single PD due to collisions from multiple PDs,then the PSE knows that there are multiple PDs on the bus. The PSE maythen act accordingly by continuing with any handshaking protocol orceasing any handshaking protocol.

Despite the initial collisions, the PDs and PSE may still eventuallycommunicate since collision avoidance protocols may then occur, such asthe various PDs and/or PSEs being controlled to randomly stagger theirrespective signals over the bus.

Provide Power, Such as PoE, Using Only One Twisted Wired Pair of theCable

In some applications, a grounded chassis or ground wire already exists.Therefore, it may be more economical for the PSE to not apply the groundvoltage over a wire pair in the Ethernet cable.

FIG. 12 illustrates a PSE 182 connected to an Ethernet bus 184 andmultiple PDs 186, 187, and 188 connected to the bus 184, where the PDs186-188 include a converter 190 that has an in-rush current limiter forhot-swapping of the PDs. The positive voltage of the PoE is providedover one twisted pair of the Ethernet cabling, and the ground voltage isprovided over an external conductor. The external conductor may be themetal chassis of an automobile or an external wire. The PDs 186-188 haveconnectors that connect to the grounded conductor.

This technique applies to non-PoE systems as well where a PD receivespower via one or more data lines.

Security Technique for PD to Ensure it has Performed Proper HandshakingProcedure

A PD may be quite valuable, such as a car radio or GPS device.Therefore, it is desirable to provide a security feature to reduce thedesirability of stealing the PD from the automobile.

FIGS. 13 and 14 illustrate a security technique wherein, only if aproper PoE protocol (or other protocol) is performed is an enablingcircuit in the PD triggered for allowing the PD to operate. The PSE 192in FIG. 14 may be conventional.

In step 194 of FIG. 13, the PSE 192 provides the conventional lowcurrent to the PD 196 (FIG. 14) during the handshaking phase. Thehandshaking may be the conventional detection/classification protocol ora non-standard protocol.

A detector 198 in the PD 196 senses the low current and uses that powerto trigger an enabling circuit 200 (such as a latch). The enablingcircuit 200 closes a switch 202 that then connects the PD's voltageconverter (or the PoE directly) to the load 204. As shown in step 206,the detector 198 may even sense that the PSE 192 is using the standardhandshaking protocol or a customized protocol before triggering theenable circuit 200.

In step 208, when the enabling circuit 200 is triggered, the PD 196 isenabled for normal operation.

In step 210, if the detector 198 does not sense the required handshakingroutine, such as if 12 or 44 volts were directly applied to the powerinput pins of the PD 196, indicative of the PD being used in anunauthorized system, the open switch 202 causes the PD to be inoperable.

This technique applies to non-PoE systems as well, where a PD receivespower via one or more data lines and there is a low current handshakingroutine used to identify the components.

Security Technique to Ensure PD Still Connected in System Before orafter Powering Up

There is a possibility that a PD may be stolen or inadvertentlydisconnected from the Ethernet system before being powered or whilebeing powered. FIG. 15 illustrates a security technique thatperiodically detects whether a PD is still connected to the PSE afterpowering up and, if not, then initiates a security routine. The routinemay also be applied prior to the PD's being powered up.

In step 214 of FIG. 15, upon the PSE and PD being powered up, aconventional handshaking routine is conducted and PoE is applied to thePD. The PSE then provides the power needed by the PD.

In step 216, periodically, such as every 20 seconds, the PSE performs aroutine that detects if the PD is an open circuit, or if no power isbeing drawn, or any other anomaly. This step may also be performed priorto the PD being powered up.

In step 218, if the PSE detects such an anomaly before or after poweringup, the PSE initiates a security routine, such as a warning to thedriver or an alarm.

This technique applies to non-PoE systems as well, where a PD receivespower via one or more data lines and there is a detection signal used todetermine whether the PD is still connected to the PSE.

PD has Standby Power Path to Low Power Components and High Power Path toHigh Power Components

Power-over-Ethernet (PoE) continues to gain popularity as products takeadvantage of DC power and high-speed data available via a single set ofwires. It is predicted that more and more of an automobile's electricalsystem will conduct data and power via a shared bus, such as aPoE-enabled Ethernet bus. The systems may have to conform to IEEEstandards for compatibility. Using a shared data and power bus reduceswiring and allows a central means of monitoring the status of thevarious systems. Many other benefits can be realized. Accordingly, newtechniques that are directed to such automobile applications are veryvaluable.

When an automobile begins operation, the automotive electronics,processors, memory, and other system functions must go through astart-up sequence. These system functions must begin the start-upsequence from either a low-power hibernation state, or a completelyunpowered state. A PD starting from an unpowered state may need to gothrough the IEEE PSE-PD handshaking protocol and complete its own powerup sequence for downstream electronics. All in all, the completeautomotive system power up sequence and boot-up can be time consumingand undesirable.

Additionally, it is common for a PD to have a low power standby mode, aspreviously described, so that time is not wasted booting up when the PDcomes out of the standby mode and draws a much higher current.

The DC-DC converter in the PD, which is typically a switching converter,is inefficient when supplying a low power due to the high frequencyswitching losses. For standby modes, it is known to provide a switchingconverter with a sleep mode, where the switching stops and the outputcapacitor supplies the current to the load. When the capacitor voltagegoes below a threshold, the switching converter turns on for a shorttime to charge the capacitor back to a starting voltage. A hysteresiscomparator is used to keep the output voltage within two limits.Switching converters with a sleep mode are well-known and conventionaland need not be further described.

In the example of FIG. 16A, the high power load 220 is separate from thelow power load 222 in the PD 224. In an automobile application, the lowpower load 222 may be a processor and/or a memory that requires littlepower (e.g., less than 1 W), especially in a standby mode, and the highpower load 220 may be a motor, an entertainment system, a safety device,lights, or other feature of the automobile.

The standby (or sleep) mode low power path 226 from the converter 227 tothe low power load 222 is separate from the high power path 228 from theconverter 227 to the high power load 220. This is so that the high powerload 220 does not receive any power during the low power mode. A switchbetween the converter 227 and the high power load 220 may evencontrollably disconnect the high power load 220 from the converter 227during the low power mode so little current is drawn in the high powerpath. The switch may be controlled by a processor in the PD 224.

As shown in FIG. 16B, instead of a single DC-DC converter 227 supplyingpower to both loads 220 and 222, the low power load 222 may insteadreceive power from a separate converter such as an LDO regulator 229 orany other power-efficient methods of voltage regulation. Therefore, aswitching regulator 231 may supply power to the high power load 220, andthe LDO regulator provides power to the low power load 222 via theseparate paths 226/228. When the low power load 222 comes out of itsstandby mode, such as when the ignition switch is turned on, the lowpower load 222 may also be powered by the switching regulator 231.

In any of the various scenarios described, it is envisioned that thehigh power load 220 is substantially off while the low power load 222 isin its standby mode, such as when the ignition switch is off, to enablethe low power load 222 to efficiently receive a low current from theconverter 227.

In one embodiment, the low power load 222 uses a different input voltagethan the high power load 220 and uses a separate converter for supplyingthe different voltage via the low current path 226.

In one embodiment, the converter 227 may be a switching regulator thatoperates in a sleep mode when supplying power to the low power load 222is in its standby mode. Such a sleep mode may be a hysteresis mode wherethe switching regulator periodically turns on (wakes up) to keep theoutput voltage between an upper threshold voltage and a lower thresholdvoltage. Such sleep mode circuits are well-known. When the PD becomesactive and the high power load 220 is to be operational, the converter227 comes out of its sleep mode to power both loads. A signal to becomefully operational may be when the automobile ignition switch is turnedon.

The low power load 222 may include standby circuitry such as memories,processors, etc. The standby circuitry can maintain information, provideprocessing functions, and retain start-up information while operating ina low-power state. Using the information retained in the standbycircuitry may significantly reduce boot up time and start-up delay.

FIG. 16C is a flowchart identifying certain steps performed by thecircuit of FIG. 16A.

In step 280, the PSE 230 may receive a signal from the PD 224 initiatinga standby mode, or the PSE 230 may transmit a signal initiating thestandby mode, or the standby mode is only communicated within the PD224. The PSE 230 continues to provide normal PoE power to the converter227. This signal may be initiated by the ignition switch of theautomobile being turned off.

In steps 282 and 284, as a result of the standby mode occurring, theconverter 227 goes into its sleep mode, which may be automatic ortriggered, and only the low power path 226 conducts the current to thelow power load 222. A switch 223 (FIG. 16B) may be provided at theoutput of the converter 227 to connect the output terminal to either ofthe two paths, depending on whether the system is in the standby mode ornot. In this way, the high power load 220 does not draw current in thestandby mode.

In steps 286, 288, and 290, when the PD 224 comes out of the standby (orlow power) mode, the converter 227 operates in its normal switchingconverter mode, and the output of the converter 227 is switched to thehigh power path 228 to power the high power load 220 and the low power(standby) load 222. This may occur when the ignition switch is turnedon. It is presumed that the low power load 222 draws, on average, morecurrent than in its standby mode.

In another embodiment, the PSE or PD sends a data signal to the lowpower load 222 to wake up prior to the high power load 220 turning on sothat no time is wasted for any booting up time of the low power load222. This data signal generated by the PSE or PD may be initiated by theignition switch being turned on.

FIG. 16A also shows the voltage converter 234 in the PSE 230 providingthe standard PoE voltage or a programmable voltage. The conventional orcustomized detection/classification circuitry 236 is shown in the PD224.

The border shown in FIG. 16A surrounding the PD 224 does not imply thatthe PD 224 is a single physical unit, such as a printed circuit board(PCB), but only indicates that the circuitry within the border isconsidered part of the PD 224. For example, the termination block 25 andthe converter 227 may be on a single PCB, and the loads 220 and 222 maybe on separate PCBs.

This technique applies to non-PoE systems as well, where a PD receivespower via one or more data lines.

Fast Collision Detection on Bus

When multiple devices are connected to an Ethernet bus or other databus, it is common for multiple devices to transmit at the same time.Such data is corrupted by the collision of the data on the bus. Varioustechniques are conventionally used to detect collisions and to staggerthe retransmissions. One way of detecting a collision is for alltransmissions to require the receiving device to acknowledge receipt ofa valid message. If the receipt signal is not generated within a certaintime window, the transmitted data is assumed to have been corrupted andthe data is then retransmitted. In all these techniques, there is adelay incurred by detecting the collision, followed by authorizingmultiple devices to retransmit their messages in a staggered fashion. Itis desirable to speed up the collision detection and retransmissionprocess.

FIGS. 17A, 17B, and 17C illustrate how the signals from multiple PDs 240and 242 connected to an Ethernet bus 243 or other bus may be summed andthe summed signals detected to determine whether a collision hasoccurred, requiring retransmission. There is no need for anyacknowledgment of receipt of a valid message for the system to know thata collision has occurred. Therefore, the retransmission may occur rightaway.

A set of allowable symbols is stored in a table 244 in each PD. Thetable 244 communicates with the data physical layer 245 in the PD. Theremay be any number of allowable symbols. A symbol may be any combinationof pulses, where each pulses may have multiple levels, such as 1-5volts. Therefore, three pulses forming a symbol may convey one of 125possible symbols. In the example of FIG. 17C, symbols formed by only twopulses are used for simplicity.

In step 246 of FIG. 17B, the PDs transmit allowable symbols on the buswithout any collisions. These allowable symbols match the allowablesymbols stored in the table 244. The symbols are detected at the PDsand/or PSEs and the appropriate functions are performed.

In step 248, the table 244 also stores disallowed symbols, which aresymbols that are not assigned any functions and should not be properlytransmitted on the bus 243. Some or all of these disallowed symbols maybe the sums of allowable symbols. In an example, a PD generates a pulseof a desired level by supplying a current to the bus 243, and theimpedance of the PD on the data line, such as 100 ohms across a twistedwire pair, generates a voltage across the pair. If multiple PDssimultaneously transmit a current, the currents are summed on the bus243 and create a voltage that is the sum of the intended pulse levels.

The allowed and disallowed symbols are selected such that the varioussums of allowed symbols equal disallowed symbols (step 250). Forexample, FIG. 17C illustrates two allowed symbols being simultaneouslytransmitted by two PDs: PD1 and PD2. The sums of the pulses in theseallowed symbols produce a disallowed symbol formed of a 5 volt pulse anda 4 volt pulse.

In step 252, this disallowed symbol is detected by the table 244, it isignored by the receiving PD(s), and the occurrence of the disallowedsymbol instantly triggers a collision avoidance routine, such as acommand to all the PDs to retransmit their data after a random time orin a certain sequence. Thus, the conventional time for detecting acollision and ordering the retransmission is greatly reduced.

FIG. 17A also shows a conventional detection/classification circuit 254,a DC-DC converter 255, and a load 256, connected to the bus 243 via aninterface circuit 257.

The above technique is independent of whether the system provides powerover data lines.

Fast Control of Bus for Transmission of High Priority Data

As discussed above, when multiple devices are connected to an Ethernetbus or other bus, it is common for multiple devices to transmit at thesame time. Such data is corrupted by the collision of the data on thebus. There is a delay incurred by detecting the collision, followed byauthorizing multiple devices to retransmit their messages in a staggeredfashion. However, in some emergency situations, such a delay becomesvery significant and even dangerous. For example, a safety feature in anautomobile, such as an air bag controller, may need instant access tothe bus to transmit a high priority message.

FIG. 18 illustrates a technique for quickly issuing an ALL STOP signal(or equivalent command signal) to all PDs on a bus, without having towait for the bus to be idle after a collision, in order to transmit ahigh priority message on the bus.

In step 260 of FIG. 18, an ALL STOP command (a symbol), for telling thePDs to not transmit on the bus, is assumed to be a combination of pulseshaving certain voltage levels. The data need not be digital. In theexample, the ALL STOP symbol is three, 4 volt pulses.

In step 262, it is assumed that a low priority PD is currentlytransmitting multi-level pulses on the bus, such as a symbol consistingof one, 3 volt pulse and two, 2 volt pulses. The low priority messagemay consist of many symbols.

In step 264, it is assumed that a high priority PD, such as an air bagcontroller PD, wishes to send a high priority message on the bus andneeds all other PDs to stop transmitting. The high priority PD does notwant to wait for the bus to be idle.

In step 266, the high priority PD detects the low priority pulses andinstantly adds or subtracts the necessary current to/from the pulses onthe bus to create the ALL STOP symbol of three, 4 volt pulses. Theresulting symbol is detected by all PDs, which instantly terminates alltransmission. The bus is now freed up without any collisions and withoutdelay waiting for low priority PDs to complete their transmissions.

In step 268, the high priority PD then transmits the high prioritymessage on the bus.

The above technique is independent of whether the system provides powerover data lines.

Any of the features described throughout this entire disclosure may becombined.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects and, therefore, the appended claims areto encompass within their scope all such changes and modifications thatare within the true spirit and scope of this invention.

What is claimed is:
 1. A Power Over Ethernet (PoE) system comprising:Power Sourcing Equipment (PSE) providing data and voltage over Ethernetwires, the PSE having a voltage source for generating a PSE voltage fortransmission on the Ethernet wires; and a Powered Device (PD) connectedto the PSE by at least the Ethernet wires to receive the data andvoltage, wherein the PD has at least a first load and a second load,wherein the first load has at least a first mode of operation whichcauses the first load to draw a first current, wherein the second loadhas at least a second mode of operation which causes the second load todraw a second current larger than the first current, wherein the PD hasat least one DC-DC converter that converts the PSE voltage into at leastone regulated voltage for supplying power to the first load and thesecond load, wherein there is a first current path to the first load anda separate second current path to the second load from the at least oneDC-DC converter, wherein the first current path supplies at least thefirst current to the first load in the first mode of operation whilesubstantially no current is supplied to the second load via the secondcurrent path while the first load is in the first mode of operation, andwherein the second current path supplies at least the second current tothe second load when the second load is in the second mode of operation.2. The system of claim 1 wherein the first mode of operation is astandby mode.
 3. The system of claim 1 wherein the first load includes aprocessor, and the first mode of operation is a standby mode for theprocessor.
 4. The system of claim 1 wherein the at least one DC-DCconverter is in a sleep mode of operation during the first mode ofoperation of the first load.
 5. The system of claim 1 wherein the atleast one DC-DC converter comprises multiple DC-DC converters, one beingconnected to the first current path and one being connected to at leastthe second path.
 6. The system of claim 1 wherein the at least one DC-DCconverter comprises a single DC-DC converter with a switchableconnection to the second load.
 7. The system of claim 1 wherein thesecond mode of operation does not occur during the first mode ofoperation.
 8. The system of claim 7 wherein the first load operates in athird mode of operation when the second load operates in the second modeof operation.
 9. The system of claim 8 wherein the third mode ofoperation draws more current than the first mode of operation.
 10. Thesystem of claim 1 wherein the system is in an automobile.
 11. The systemof claim 1 wherein the at least one DC-DC converter comprises at least aswitching regulator and a low drop out (LDO) regulator, wherein the LDOregulator supplies current to the first load via the first current pathduring at least the first mode of operation.
 12. The system of claim 1wherein the first mode of operation is a standby mode, the systemfurther comprising a first circuit that causes the first load to comeout of its standby mode and operate in a third mode of operation priorto the second load beginning its second mode of operation.
 13. Thesystem of claim 12 wherein the first circuit comprises an ignitionswitch for an automobile.
 14. A method performed by a Power OverEthernet (PoE) system comprising: providing, by a Power SourcingEquipment (PSE), data and voltage over Ethernet wires, the PSE having avoltage source for generating a PSE voltage for transmission on theEthernet wires; converting the PSE voltage to a first regulated voltageby at least one DC-DC converter in a Powered Device (PD), the PD beingconnected to the PSE by at least the Ethernet wires; operating, during astandby period, a first load in the PD, wherein the first load operatesin a standby mode of operation during the standby period and draws afirst current from the at least one DC-DC converter via a first currentpath; maintaining idle a second load in the PD during the standby mode,wherein the second load draws substantially no current during thestandby mode; causing the first load to come out of the standby mode andinto an active mode; and causing the second load to draw a secondcurrent from the at least one DC-DC converter during a second mode ofoperation while the first load is in its active mode, wherein the secondcurrent is supplied to the second load via a second current pathdifferent from the first current path.
 15. The method of claim 14wherein the second load is disconnected from the at least one DC-DCconverter during the standby period.
 16. The method of claim 14 whereinthe first load includes a processor, and the standby mode is a standbymode for the processor.
 17. The method of claim 14 wherein the at leastone DC-DC converter is in a sleep mode of operation during the standbymode.
 18. The method of claim 14 wherein the at least one DC-DCconverter comprises multiple DC-DC converters, one being connected tothe first current path and one being connected to at least the secondpath.
 19. The method of claim 14 wherein the at least one DC-DCconverter comprises a single DC-DC converter with a switchableconnection to the second load.
 20. The method of claim 14 wherein thesecond mode of operation does not occur during the standby mode.
 21. Themethod of claim 20 wherein the first load operates in a third mode ofoperation when the second load operates in the second mode of operation.22. The method of claim 21 wherein the third mode of operation drawsmore current than the first mode of operation.
 23. The method of claim14 wherein the system is in an automobile.
 24. The method of claim 14wherein the at least one DC-DC converter comprises at least a switchingregulator and a low drop out (LDO) regulator, wherein the LDO regulatorsupplies current to the first load via the first current path during atleast the standby mode.
 25. The method of claim 14 further comprising afirst circuit that causes the first load to come out of its standby modeand operate in a third mode of operation prior to the second loadbeginning its second mode of operation.
 26. The method of claim 14wherein the first circuit comprises an ignition switch for anautomobile.